Sonny Bill Williams knows there is a chance he could be playing his last game of rugby in New Zealand this Friday night.

But the player who will head to Japan to take up a lucrative new contract after the Super Rugby season is trying to put that thought squarely to one side as he prepares for the Chiefs' semifinal against the Crusaders at Waikato Stadium.

Rather than allowing the emotion of that to overwhelm him, he wants to harness it to bring the best out in his performance as the Chiefs strive for just their second visit to the grand final in 17 years.

"I don't want to get too emotionally attached to it, because it could be my last week here, but I'm just trying to turn all those emotions into motivation," Williams said yesterday at the start of the Chiefs' biggest training week of their season to date.

"I want to come in, do all my work and try and build like I haven't done it before - try and tick all those boxes.

"And then hopefully run out there on Friday night fizzing and just do my role really well."

Williams is no stranger to big matches, having played for the Crusaders last season, experienced the All Blacks' World Cup-winning campaign and been through some big playoff games on the way to winning the NRL title with the Canterbury Bulldogs in 2004 as a young rookie. He knows what approach works best in these situations.

"You've still got to do what you do, keep it simple and nail everything you do during the week so you're confident.

"That's probably what I will do. Just nail everything that I usually do and go into the game knowing I've done everything I can, then just play footy and back myself."

Williams predicted the semifinal would be a step up from any other game the Chiefs had played all year, including the hugely intense last clash between the two sides at Waikato Stadium 2 weeks ago.

"You've just got to be at your best and in those times when you're in that dark place that's when you use it as well to try and pull something out, keep pushing hard, keep getting up off the deck and making that extra tackle - just things like that," he said.

Williams said the Chiefs players had every reason to go into the match with belief in their own ability.

"Be confident, we deserve to be here and we've just got to play footy."

His experience with the Crusaders who had enormous self-confidence told him that type of approach could certainly be transferred to the Chiefs.

"But in saying that it's a lot of hard work. The Crusaders have got internationals all over the field and are in really good form so we're going to have play better than we ever have."

The extra week off the second-seeded Chiefs got while their opponents had to play a qualifying match had been invaluable for allowing players to shake off niggling injuries.

"We've got a whole week of extra training in, working those combinations, and we'll take that onto the pitch on Friday," Williams said.

While much talk in the buildup to the semifinal surrounds how the Chiefs can match up to the intensity of the All Blacks-laden Crusaders pack, particularly at set-piece time, Williams said the backs had to be ready to take their chances and make sure they finished off every opportunity they got.

"Just being on our toes and taking every opportunity and making every opportunity count. That's something we haven't done in the last couple of weeks and that started against the Crusaders in that last five minutes when I didn't pass the ball when we had a two-man overlap.

"Just little things like that have crept into our game I guess and that's why it's been good to have these two weeks to assess ourselves and now know what we have to do."